1. Field of the Invention
The present invention relates to a field effect transistor, and more particularly, to a switching field effect transistor (FET) using abrupt metal-insulator transition.
2. Description of the Related Art
Metal Oxide Semiconductor Field Effect Transistors (MOSFETs) have been widely used as micro and super-speed switching transistors. A MOSFET has two pn junction structures showing linear characteristics at a low drain voltage as a basic structure. However, when a channel length is reduced to about 50 nm or below as the degree of integration of a device increases, an increase in a depletion layer changes the concentration of a carrier and an decrease of the depth of the gate insulator remarkably makes current flowing between a gate and a channel.
To overcome this problem, IBM institute has performed Mott FETs using the Mott-Hubbard insulator in a channel layer in reference xe2x80x9cD. M. Newns, J. A. Misewich, C. C. Tsuei, A. Gupta, B. A. Scott, and A. Schrott, Appl. Phys. Lett. 73, 780 (1998)xe2x80x9d. The Mott-Hubbard insulator undergoes a transition from an antiferromagnetic insulator to an metal. This transition is called the Mott-Hubbard metal-insulator transition in reference xe2x80x9cJ. Hubbard, Proc. Roy. Sci. (London) A276, 238 (1963), A281, 401 (1963)xe2x80x9d. This is a continuous (or second order) phase transition. Unlike MOSFETs, Mott FETs perform an ON/OFF operation according to metal-insulator transition and do not have a depletion layer, thereby remarkably improving the degree of integration of a device and achieving a higher-speed switching characteristic than MOSFETs.
Since Mott-Hubbard FETs use continuous metal-insulator transition, charges used as carriers should be continuously added until the best metallic characteristics reach. Accordingly, the added charges must have a high concentration. Generally, charges N per unit area can be expressed by Equation (1).                     N        =                              ϵ            ed                    ⁢                      V            g                                              (        1        )            
Here, xe2x80x9c∈xe2x80x9d denotes the dielectric constant of a gate insulator, xe2x80x9cexe2x80x9d denotes a basic charge, xe2x80x9cd,xe2x80x9d denotes the thickness of the gate insulator, and xe2x80x9cVgxe2x80x9d denotes a gate voltage.
For example, in the case of La2CuO4, which is one of the materials falling under the group Mott-Hubbard insulator, when holes are added to La2CuO4, the characteristics of La2xe2x88x92xSrxCuO4(LSCO) appear, and a metal having best hole carriers at x=0.15 (15%) is obtained. Here, the added holes become carriers. Generally, x=0.15 is a high concentration, so if the N value increases, the dielectric constant of the gate insulator increases, the thickness of the gate insulator decreases, or the gate voltage increases. However, when the dielectric constant is too great, the fatigue characteristics of a dielectric sharply worsens during a high-speed switching operation, thereby reducing the life of a transistor. Moreover, there is a limit in decreasing the thickness of the gate insulator due to limitations in fabrication processes. In addition, when the gate voltage increases, power consumption also increases, which makes it difficult to be the transistor with a low power.
To solve the above-described problems, it is an object of the present invention to provide a switching field effect transistor using abrupt metal-insulator transition so that the field effect transistor shows metallic characteristics even if holes of a low concentration are added thereto.
To achieve the above object of the invention, there is provided a field effect transistor including a substrate; a Mott-Brinkman-Rice insulator formed on the substrate, the Mott-Brinkman-Rice insulator undergoing abrupt metal-insulator transition when holes add therein; a dielectric layer formed on the Mott-Brinkman-Rice insulator, the dielectric layer adding holes into the Mott-Brinkman-Rice insulator when a predetermined voltage is applied thereto; a gate electrode formed on the dielectric layer, the gate electrode applying the predetermined voltage to the dielectric layer; a source electrode formed to be electrically connected to a first portion of the Mott-Brinkman-Rice insulator; and a drain electrode formed to be electrically connected to a second portion of the Mott-Brinkman-Rice insulator.
Preferably, the substrate is formed of SrTiO3.
Preferably, the Mott-Brinkman-Rice insulator is formed of LaTiO3, YTiO3, Ca2RuO4, Ca2IrO4, V2O3, (CrxV1xe2x88x92x)2O3, CaVO3, SrVO3 and YVO3.
Preferably, the dielectric layer is formed of Ba1xe2x88x92xSrxTiO3 or dielectric materials.
Preferably, the source electrode and the drain electrode are separated from each other by the dielectric layer.